What Are Black Holes?

The spoken lesson

"A black hole is an extremely compact concentration of mass. Its event horizon is a boundary from inside which light and information cannot escape to a distant observer. The event horizon is not a solid surface. A black hole itself does not shine, but gas and dust orbiting outside it may become extremely hot and bright in an accretion disk. Astronomers detect black holes through orbiting stars, glowing material, gravitational lensing, gravitational waves, and other effects on the surroundings. Black holes are not cosmic vacuum cleaners, and they are not proven portals. From far enough away, their gravity behaves like that of another object with the same mass. Black holes are detected through gravity, heated surroundings, distorted light, and ripples in spacetime." DESIGN REQUIREMENTS: Use accurate anatomy, calm backgrounds, and evidence-based detection. Avoid horror, people falling, suction effects, portal imagery, visible material inside the event horizon, or treating a fabric analogy as literal spacetime.